Closing device for the closing tools of a bag-packing machine

ABSTRACT

The invention relates to a closing device for the closing tools of a bag-packing machine.  
     In known machines of this type, the closing tools are actuated by mechanical means such as lever systems, or pneumatic or hydraulic systems. These drive systems do not allow the machine to achieve high yields, since the mass of the components that must be moved back and forth is too great.  
     The goal of the invention is to allow the machine to achieve a greater bag production and an enhanced precision in the movements executed by the tools, while also reaching a greater and higher closing force, among other things. This is accomplished in that the guide elements ( 18, 19, 20, 21; 34 ) of the tools ( 11, 12 ) take the form of toothed racks, while at least one toothed rack is driven by a motorized pinion ( 22, 23; 26, 27, 28, 29; 36 ).  
     The motors employed will preferably be digital servomotors.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority under 35 U.S.C. §119 of Swiss Patent Application No. 2000 1292/00, filed on Jun. 30, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a closing device for the closing tools of a bag-packing machine, as described in the preamble of claim 1.

[0004] 2. Discussion of Background Information

[0005] Bag-packing machines of the indicated type, as they are known from practice and as heavily represented in the patent literature (e.g., DE C 303 1399), generally comprise a housing in which the operating components are installed. The most important operating components are the film web feeder with film roller and with guidance and transport rollers; the so-called format aggregate, with a filling tube for filling the product into a bag produced from a flexible web of film, and a forming shoulder, over which the web is guided in order to form it into a tube; a longitudinal closing device, for producing the bag's longitudinal seam; and a transverse closing device, for producing the transverse seam, i.e., for closing the bag.

[0006] The closing tools, primarily the transverse closing tools, perform opposite opening and closing movements, while the relatively large mass of hot tools must be moved back and forth over relatively large distances (on the order of 125 mm) up to one hundred eighty times per minute. These movements must be very precise, since the quality of the produced bags depends heavily on the so-called closing pressure of the interacting tools. The quiet operation of the machine must be assured despite the relatively large masses being moved.

[0007] The machines known to the prior art solve the problem posed by the demanding movement of the closing tools of the bag-packing machine by means of a lever system, e.g., knee levers, or by use of pneumatic or hydraulic drive systems, or with toothed belts.

[0008] All of these known systems expose their limitations, however, as soon as the production speed reaches certain values, since the components needed for driving the tools (levers, cylinders, pistons, transmission components, etc.) have too great a mass and therefore generate large dynamic forces. The result is a limit to the production speeds of the machine, which consequently cannot be fully utilized. Furthermore, these components require a great deal of space, so that the entire machine must have greater depth.

SUMMARY OF THE INVENTION

[0009] The purpose of the present invention is to overcome these limitations in the existing technology for the closing devices of tools belonging to bag-packing machines, primarily by reducing the mass of the tool components that move back and forth. In the solution according to the invention, furthermore, a greater precision in the tool movement is achieved, as well as a more precise adjustment of the closing force. In addition, as will be explained in detail below, it will be possible to run the machine in continuous operating mode. “Continuous operating mode” is understood to be machine operation in which the movement of the packaging film is never interrupted, i.e., in which the film is continually advanced, even during the closing operation performed by the longitudinal closing device and the transverse closing device. It should be noted here that in conventional bag-packing machines the formation of the closing seams takes place when the bag being formed is at rest; the film must be braked during each machine cycle (or, as the case may be, during each instance of bag production) and then reaccelerated. Every skilled artisan knows that this braking and reaccelerating of the film represents a stress on the film and the filling material. Due to the fact that, according to the invention, the closing tools have a small mass, it now becomes possible to solve this problem and to guarantee the continuous operation of the machine. All of these goals are now fulfilled with a closing device of a generic type according to the preamble of claim 1, which is characterized by the features of characterizing portion of claim 1.

[0010] The guidance of the closing tool by means of at least one guide element designed as a toothed rack, where the toothed rack is driven by a motorized pinion, represents a solution that is far superior to previous solutions, one whose effects will be described in greater detail below on the basis of several exemplary embodiments. It should be immediately noted, however, that such guide elements are precise and extremely low in mass and that the use of pinions of the smallest diameter makes it possible to achieve a very high closing force, while relatively small forces are applied to the closing device. The invention will now be described on the basis of several illustrated examples, in the process of which several advantages of the invention will emerge.

[0011] Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

[0013] The figures show:

[0014]FIG. 1 the front view of a bag-packing machine according to the invention, in simplified form, i.e., without the operating components that are inessential to the invention;

[0015]FIG. 2 a side view of the machine shown in FIG. 1, in a simplified and purely schematic depiction;

[0016]FIG. 3 a top view of a first embodiment of the closing device according to the invention, with two synchronized motors for the drive;

[0017]FIG. 4 a top view of another embodiment of the closing device according to the invention, with four synchronized motors for the drive;

[0018]FIG. 5 a top view of another embodiment of the closing device according to the invention, with a single motor for the drive.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0019] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

[0020]FIGS. 1 and 2 show the basic design of a bag-packing machine, viewed from the front and from the side, in a simplified, purely schematic depiction. To this end, the figures contain only the parts necessary for explaining the invention. Other parts of the machine (e.g., the film feeder, the scale, the forming aggregate, etc.) that play no role in the invention are omitted in order not to complicate the description unnecessarily and make it unreadable. The bag-packing machines to which the present invention applies are intimately known to one skilled in the art, from both actual practice and the patent literature, so that their complete description here seems unnecessary. As an example of such machines we would like to mention DE 3031 399 A1, which relates to a process and a device for forming, filling, and closing packages.

[0021]FIGS. 1 and 2 depict two horizontal beams 1, to which a vertical column 2 is secured in either case, roughly in the middle. On their unattached upper end, the two columns 2 are connected by a yoke 3. The beams 1, the columns 2, and the yoke 3 form the framework of the machine, to which the actual operating components are attached. Thus, two vertical guide elements are applied to the columns 2, to which the longitudinal closing device 5 and the transverse closing device 6 are attached. These closing devices 5 and 6 relate to the subject matter of the invention and are therefore described in greater detail below, both in terms of their design and their function.

[0022] Two support rods 7 can be seen on the yoke 3; these elements support two more operating components (not shown) of the machine, namely the so-called forming aggregate, with the filling tube, and the film-forming shoulder. All of these components are known to one skilled in the art and do not require special explanation and description. Also shown in FIG. 1 is the control box 8 for controlling the machine motors. In contrast, the entire film guidance system and the scales are not shown. The former would lie on the left side of FIG. 2, while the second is positioned above the yoke, if need be, on the column 2 itself. All of this is conventional and well-known.

[0023] The present invention relates only to the closing devices of the closing tools of the machine or, more precisely, to the manner in which the closing tools are guided and driven. At this point, it should be explained that a bag-packing machine of the type under consideration generally has two closing devices, namely a longitudinal closing device 5 and a transverse closing device 6. Both closing devices are basically identical in design, even if the position of the closing device, in keeping with its task, differs. Thus, the longitudinal closing device 5 comprises a heated tool 9 (FIG. 2) that stands in vertical position and a counterstay 10. Between the two tools 9 and 10 lies the filling tube (not shown), by means of which the material to be packaged is fed into the bag. The role of the tool 9, which is a heated tool, is welding or, as is also said, sealing the so-called longitudinal seam of the bag and thus converting the open packaging film into a closed tube. In the context of the invention, the important fact is only that the two tools 9 and 10 belonging to the longitudinal closing device must be precisely guided and must move in opposite directions, towards and away from each other, in a synchronized fashion.

[0024] The transverse closing device 6 differs from the longitudinal closing device 5 just described only in the type and position of the two tools forming it, which in this case are heated, horizontally inclined tools 11 and 12. The other components of the transverse closing device 6 precisely correspond to those of the longitudinal closing device, with respect to both the guide elements and the drive components. The fact that the distances traversed by the components (the tools 9 and 10 or 11 and 12) can differ in length (as a rule, the tools of the transverse closing device 6 cover longer distances than those of the longitudinal closing device 5) does not play an essential role in the invention and can be ignored as a difference between the two closing devices. For this reason, the invention and its variants will only be described in detail on the basis of the transverse closing device 6; what is said in the description of the transverse closing device 6 also applies to the longitudinal closing device 5, however.

[0025] To gain further acquaintance with the invention, FIG. 3 should be consulted, where the elements of a transverse closing device according to the invention are shown in top view. Thus, FIG. 3 is a view from above of the object of FIG. 1, in which, however, the longitudinal closing device 5 and the yoke 3 have been omitted. In FIG. 3, the number 13 designates a support (a support plate), which is guided vertically into the guide elements 4. The support 13 is provided with four parallel, horizontal holes, into which are inserted the guide tubes 14 and 15, or 16 and 17, of the tool 11 or 12. The guide tubes 14 to 17 are tubes in which the corresponding guide elements 18 and 19 or 20 and 21 are guided. The guide tubes 14 to 17 are relatively long and thus guarantee the precise guidance of the guide elements 18 to 21 and thus of the tools 11 and 12. It is decisive for the proper functioning of the closing device that the tools 11 and 12 are moved in absolutely parallel fashion and that the so-called closing pressure (i.e., the force with which the tools 11 and 12 are pressed together) can be controlled. Only in this way can a clean and reproducible bag seam be guaranteed.

[0026] The guide elements 18 to 21 are formed as toothed racks, at least over a certain portion of their length, i.e., they have a gearing (not shown in FIG. 3).

[0027] In the exemplary embodiment shown in FIG. 3, which should be viewed as a preferred variant of the invention, the toothed racks of the guide elements 18, 20 engage with a first pinion 22, while the toothed racks of the guide elements 19, 21 engage with a second pinion 23. The pinions 22 and 23 each rotate around their vertical axes. Each pinion 22, 23 is driven by its own motor 24, 25, which is placed in vertical position beneath the support 13. In FIG. 3 the motor 24, 25 is depicted schematically as a rectangle, a convention that will be retained in the other exemplary embodiments that are depicted.

[0028] When the motors 24 and 25 are operated in strictly synchronous fashion but in opposite directions, they will move the guide elements 18 and 19 or 20 and 21 in the same direction by means of the pinions 22 and 23. Depending on the rotational direction of the motors 24 and 25, the tools 11 and 12 will be moved toward each other or away from each other, i.e., they will perform a closing movement or an opening movement. Naturally these movements can be more precisely controlled the greater the absence of play in the guide elements 18 and 21 and the greater the operational precision in the motors 24 and 25. For this reason, high requirements are placed on the motors 24 and 25 and on their control, as will become clear below. In this solution, the successful synchronization of the motors 24 and 25 plays an especially large role. It should also be noted that, in the solution according to FIG. 3, the two tools 11 and 12 can only perform a movement in opposite directions. They have a rigid kinematic coupling via the pinions 22 and 23. This is a limitation which can be disadvantageous in certain cases and, for this reason, FIG. 4 shows a variation of the invention in which the tools 11 and 12 (in the figures identical numbers always refer to identical components) can also execute a simultaneous movement in the same direction. Without describing the advantages provided by these tool movements in the same direction, advantages which are not the object of this invention, it will only be noted that this capability can be advantageous, e.g., in the production of so-called standing bags, i.e., bags that have a flat base.

[0029] In order to achieve this capability, each guide element 18, 19, 20, and 21 is driven by its own pinion 26, 27, 28, 29. Four motors are naturally required in this case, which must run in strictly synchronous fashion, so that the closing process for the bag seam can run in a problem-free manner. To be sure, this can be done easily today with the use of digital servomotors, which can be controlled very precisely, most of all when use is made of fiber optic technology in providing the servomotors with cables. Thus, use can be made of so-called real time operation, a concept with which every skilled artisan in control technology today is acquainted, according to which the movements of a majority of motors can be controlled with extreme precision, so that absolute synchronization of the movements can be practically realized. In a preferred variant of the invention, therefore, the motors 30, 31, 32, and 33 of the pinions in the solution according to FIG. 4 are digital servomotors with fiber optic cabling.

[0030] The solution shown in FIG. 4 meets the highest requirements with respect to the freedom of movements of the tools 11 and 12, since it allows their independent movement, and also offers a high adjustment capability. Each tool 11, 12 can, e.g., exhibit its own movement profile, i.e., can be accelerated or delayed according to a special curve and can also move at its own speed. This advantageous variant determines the price of the device.

[0031] The present invention can be applied in another variation, however, for a closing device which is driven by a single motor. This kind of motor must be subject to precise control if good seams are to be provided, but does not have to be synchronized, since the motor runs the device alone. Involved here is a less costly solution to the problem, which in very many cases is able to meet the demands posed by actual practice. This solution is shown in FIG. 5, which depicts a closing device whose basic design in terms of guide elements and pinions resembles the solution of FIG. 3. Identical components are designated by identical numerals here as well.

[0032] The difference between the solutions shown in FIGS. 3 and 5 lies in the fact that the pinions 22 and 23 in FIG. 5 are not driven by their own motor, unlike the corresponding pinions 22 and 23 in FIG. 3. The pinions 22 and 23 in FIG. 5 serve only to kinematically couple the corresponding guide elements 18 to 20 and 19 to 21 or, stated differently, to transmit the movement of the guide element 20 to the guide element 18 and of the guide element 21 to the guide element 19. In this case, another (third) guide element 34 is provided in the center of the tool 12 for the movement of the closing device; this guide element 34 is conducted in its guide tube 35 and also takes the form of a toothed rack. A pinion 36 is driven by a motor 37 to execute a very precise back-and-forth movement. The advantage of this solution rests primarily in the presence of a single motor 37, which does not have to be synchronized with other motors belonging to the closing device. However, it should be possible to very precisely control the motor 37 (as with the motors in the other solutions depicted here) if the goal of the solution is, e.g., to realize a selected movement profile and/or to guarantee a predetermined closing force. The use of a digital servomotor for the motor 37 is therefore conceivable in this case as well.

[0033] Another advantage of the solution according to the invention is evident in the fact that the use of directly driven pinions for the drive of the tools 11 and 12 permits very high closing forces to be achieved between the tools 11, 12, without having to apply high torques. As shown by computation and by experience, even with a pinion of about 30 mm diameter it is possible to achieve programmable closing forces of greater than 12,000 N, while closing forces of about 5,000 N were known up to now in the transverse closing range.

[0034] Another advantage of the invention, which is a direct consequence of the small mass of the closing tools, rests in the capability (schematically depicted in FIGS. 2 and 3) of vertically shifting the entire apparatus, both the longitudinal closing device 5 and the transverse closing device 6, along the guide elements 4. To this end (and as described here only for the transverse closing device) a motor 38 is provided which drives two pinions 40 and 41 by means of a horizontal shaft 39. The pinions engage with two vertical toothed racks, which are furnished in the guide elements of the support 13. In this manner, the entire transverse closing device 6 can be moved up and down in the bag production cycle and in coordination with the longitudinal closing device 5. This permits the continuous operation of the machine, since the longitudinal seam of the bag must not be formed when the machine is at rest. Indeed, during formation of the seam, the longitudinal closing tool follows the progressing movement. The vertical movement of the transverse closing seam 6 offers advantages for the fabrication of the so-called standing bag, whose description, however, would exceed the bounds of the current presentation. What is important for the invention is simply the fact that such vertical movements executed by the devices in the bag production cycle become naturally possible due to the severe reduction in mass of the closing devices set in motion—something that heretofore was impossible, since it would have required overcoming excessive forces. This opens entirely new paths to bag manufacturers and permits them to significantly increase the production of their machines.

[0035] Overall, it is possible to manufacture better bags thanks to the invention, since the closing movements and the closing forces can be adjusted with extreme precision and the closing tools can execute vertical movements. The overall result is an increased machine production vis-a-vis the prior art, with a constant and high bag quality.

[0036] It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

[0037] Designation of Figures 1 beam 2 column 3 yoke 4 guide elements 5 longitudinal closing device 6 transverse closing device 7 support rod 8 control box 9 tool of the longitudinal closing device 10 filling tube counterstay 11 tool of the transverse closing device 12 tool of the transverse closing device 13 support 14 guide roller 15 guide roller 16 guide roller 17 guide roller 18 guide element 19 guide element 20 guide element 21 guide element 22 pinion 23 pinion 24 motor 25 motor 26 pinion 27 pinion 28 pinion 29 pinion 30 motor 31 motor 32 motor 33 motor 34 guide element 35 guide roller 36 toothed pinion 37 motor 38 motor 39 horizontal shaft 40 pinion 41 pinion 

What is claimed:
 1. Closing device for the closing tools of a bag-packing machine with two tools, at least one of which is heated, which tools are moved towards and away from each other in an opposite and synchronized fashion and are guided within at least two guide elements, characterized in that the guide elements (18, 19, 20, 21; 34) of the tools (11, 12) take the form of toothed racks and at least one toothed rack engages with a motorized pinion (22, 23; 26, 27, 28, 29; 36) to provide the opposite and synchronized movement.
 2. Closing device according to claim 1, characterized in that each tool (11 or 12) is guided by two guide elements (18, 19 or 20, 21) which lie on either side and take the form of toothed racks and each guide element is driven by a motorized pinion (26, 27, 28, 29).
 3. Closing device according to claim 1, characterized in that each tool (11, 12) is guided by means of two guide elements (18, 19 or 20, 21) which lie on either side and take the form of toothed racks, and the two toothed racks (18, 20; 19, 21) of the same side of the two tools (11, 12) are driven by means of a single motorized pinion (21; 23).
 4. Closing device according to claim 1, characterized in that one (12) of the two tools (11, 12) is guided by means of three guide elements (20, 21; 34) that take the form of toothed racks, while two guide elements (20, 21) lie on either side of the tool (12), while the third guide element (34) lies on the center plane of the tool (12), and the second tool (11) is guided by means of guide elements (18, 19) that take the form of toothed racks, and the third guide (34) of the first tool (12) is driven by a motorized pinion (36), while the two guide elements (18, 20; 19, 21) lying on either side of the tools and belonging in either case to one of the two tools (11, 12), are kinematically coupled as toothed racks by means of a pinion (22; 23).
 5. Closing device according to claim 1, characterized in that each motorized pinion (22, 23; 26, 27, 28, 29) is driven by a digital servomotor (24, 25; 30, 31, 32, 33; 36).
 6. Closing device according to claim 2, characterized in that the motors (24, 25; 30, 31, 32; 33; 36) that drive the toothed racks are coupled with each other and with the corresponding control system by means of fiber-optic cables for real-time operation.
 7. Closing device according to claim 5, characterized in that the digital servomotor (24, 25; 30, 31, 32, 33; 36) is set for adjusting the movement profile of the corresponding tool (11, 12).
 8. Closing device according to claims 5, characterized in that the digital servomotor (24, 25; 30, 31, 32, 33; 36), or the digital servomotors, can be modified in order to adjust the closing force of the tool, which is programmed by means of the current.
 9. Closing device according to claim 1, characterized in that the motorized pinion has a diameter of less than 30 mm. 